No need to, just stick with a small Ecsenius species: Tailspot, twinspot, lined. I prefer the tailspot over the rest for a nano tank.I may skip the Blenny all together
You can also look at things like Randals / Golden assessor (often swims inverted), pinkstreak wrasse as others have noted, many of the nano gobies (especially greenbanded - Tigrigobius multifasciatus ). Any ocellaris morph should be fine in a 30L long term, the female won't get larger than 3-4", but they can get somewhat aggressive when spawning.